Materials fashioned into a structure with a periodic arrangement of mesopores, (e.g. MCM 41), represent a special class of compounds that have realized novel applications in catalysis, separation science, and chemical sensing, (see Kresge, C. T., Leonowicz, M., Vartuli, J. C., Beck, J. C. Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature 359, 710-712 (1992)). Such compounds consist of condensed SiO4 building units linked via Si—O—Si bonds.
In contrast, periodic mesoporous organosilicas (PMO's) consist of SiO3R building blocks, whereby R is an organic group bridging the Si atoms in the form Si—R—Si. They have attracted attention because their bridging organic groups inside the channel walls of the pores provide them with distinct chemical and physical properties (see Asefa, T., Ozin, G. A., Grondey H., Kruk, M., Jaroniec, M. Recent developments in the synthesis and chemistry of periodic mesoporous organosilicas. Stud. Surf. Sci. Catal. 141, 1 (2002)).
The organic groups determine the desired properties of the material, as ‘property carriers’. Accordingly, a higher number of organic groups inside the channel walls of a PMO would be highly desirable, because improved and novel materials properties can be expected and realized. This goal can be achieved by the use of cyclic (SiR)n units with organic groups R bound to Si through Si—C bonds as building blocks for periodic mesoporous organosilicas, which is the main part of the invention.
Mesoporous silica based films are interesting for applications as low dielectric constant (k) materials because porosity decreases the k values as air has a k value of 1.01 whereby dense silica has a k value of ca. 4.5. However the k values of meso-silica are very humidity sensitive. It has been shown that the incorporation of terminal organic groups like CH3 bound to Si in meso-silica networks is beneficial for both further decreasing the k values and making it less moisture sensitive. However the mechanical stability is reduced thereby limiting the number of CH3 groups that can be incorporated into meso-silica. Therefore it is very desirable to develop new silica based mesoporous films having a very high number of bridging organic groups.